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 Table of Contents  
REVIEW ARTICLE
Year : 2017  |  Volume : 14  |  Issue : 1  |  Page : 1-7

Diagnostic anatomy of the maxillofacial region on orthopantomograph


1 Department of Oral Diagnostic Sciences, Faculty of Dentistry, Bayero University; Department of Oral and Maxillofacial Radiology, Aminu Kano Teaching Hospital, Kano, Nigeria
2 Department of Radiology, Bayero University, Aminu Kano Teaching Hospital, Kano, Nigeria
3 Department of Anatomy, Bayero University, Kano, Nigeria
4 Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria

Date of Web Publication7-Apr-2017

Correspondence Address:
Babatunde Olamide Bamgbose
Department of Oral Diagnostic Sciences, Faculty of Dentistry, Bayero University, Kano
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0331-8540.204079

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  Abstract 

The purpose of the present article was to review the physics and radiation factor of the orthopantomograph and to describe the diagnostic anatomy visualised on the imaging modality. Literature search was done via PubMed, EMBASE, Cochrane electronic databases and Google Scholar. The keywords for the search were orthopantomograph, anatomy, maxillofacial region and physics. The search was restricted to articles written in English Language and published within the years 1940–2016. The search was further limited to review, free full-text articles. The available literature was reviewed, and the physics and radiation exposure of patients undergoing orthopantomograph imaging were discussed. The radiation exposure was compared to the complete mouth series intra-oral periapical radiographs. Furthermore, the diagnostic anatomy of the maxillofacial region, as visualised on the orthopantomograph, was reviewed. The clinical relevance of the various anatomic structures was also discussed. The knowledge of maxillofacial anatomy on the orthopantomograph can be challenging due to distortion and superimposition of anatomic structures. However, a good understanding of the normal enables the clinician to identify the abnormal.

Keywords: Maxillofacial anatomy, orthopantomograph, physics


How to cite this article:
Bamgbose BO, Ismail A, Yahaya AI, Oginni FO. Diagnostic anatomy of the maxillofacial region on orthopantomograph. Niger J Basic Clin Sci 2017;14:1-7

How to cite this URL:
Bamgbose BO, Ismail A, Yahaya AI, Oginni FO. Diagnostic anatomy of the maxillofacial region on orthopantomograph. Niger J Basic Clin Sci [serial online] 2017 [cited 2017 Oct 21];14:1-7. Available from: http://www.njbcs.net/text.asp?2017/14/1/1/204079


  Introduction Top


Diagnosis embodies the art, science and the clinical judgement in arriving at a clinical definition of the presenting complaint of the patient.[1] Radiology is an important component of diagnostic sciences, and it is the responsibility of the requesting clinician to interpret the complete data set he/she has prescribed.[2] Where the image requires higher skills for interpretation, the requesting clinician should refer the images to a radiologist for expert interpretation.[2] This approach does justice to the images and ensures no diagnostic feature is overlooked.

Diagnostic evaluations of a three-dimensional object on a two-dimensional image, such as orthopantomograph, can be challenging. Quite a few young dental and medical professionals lack the familiarity and experience to confidently identify each anatomic component on the orthopantomograph.[3] This is more so in sub-Saharan Africa where oral and maxillofacial radiologists are few and orthopantomograph machines are not readily available in the dental schools.

The orthopantomograph is of considerable value in maxillofacial and dental diagnostics. It is useful in the assessment of growth and development and in the evaluation of pathoses such as abnormal ectopic eruption and impactions, cysts and neoplasms, congenital absence of teeth, premature loss, prolonged retention of teeth, ankyloses and maxillofacial trauma.[1],[4] In the present article, the authors provide a narrative review of the physics of the orthopantomograph and the radiologic appearance of anatomic structures of the maxillofacial and head and neck regions.


  Materials and Methods Top


The present study was designed as a narrative review of the physical principles and the maxillofacial anatomy as visualised on the orthopantomograph. Literature was selected through PubMed search, Google Scholar, EMBASE and Cochrane Central Register electronic databases. Keywords included orthopantomograph, physics and maxillofacial anatomy. Boolean operator 'AND' was used to combine the searches. The search was restricted to articles written in English Language and published within the years 1940–2016. The search was further limited to review, free full-text articles. Manual search was done in major anatomy journals and textbooks. Thirty-four articles were selected for review out of 210. The articles selected focussed on the anatomy and clinical significance of imaging the maxillofacial region. The remaining articles were too broad in approach to adequate address the maxillofacial anatomy. These articles highlight the clinical significance of the maxillofacial structures as visualised on the pantomograph. In addition, materials were obtained from the Library of the Oral and Maxillofacial Radiology Department of the University of Iowa, Iowa City, USA. The included publications were clinical and human anatomy studies.

The authors attempted to describe the anatomy of the maxillofacial region as visualised on the orthopantomograph, while also indicating the diagnostic importance of such structures.


  Results Top


In total, 38 articles were obtained and reviewed. The articles were filtered to include review, full text and human subject studies. The peculiarities of the maxillofacial anatomy and its clinical significance were discussed. The Paatero projection geometry incorporating both eccentric and centric motions and the amount of radiation, the patient is exposed to in comparison with a complete mouth series of periapical radiography were discussed.

Physical principles of orthopantomograph

The goal of orthopantomography is to obtain a sharp image of the dentoalveolar complex, investing tissues and associated structures such as sinuses, temporomandibular joint (TMJ), nasal cavity, conchae, stylohyoid complex, cervical spine and airway, by blurring out all intervening structures.

Paatero,[5],[6] a finnish scientist, adapted the medical radiographic process of tomography to the unique paraboloid maxillofacial system and craniofacial complex. To obtain a sharp image, the rotation of the receptor, the patient, and the X-ray tube must be precisely coordinated. Paatero combined the concentric and eccentric principles with three centres of rotations - one for each buccal segment and one for the anterior segment [Figure 1a]. This technique produced an image in harmony with the actual shape of the maxillofacial complex, with less distortion of the structures.[1],[5],[6],[7]
Figure 1a: Using the center of rotation (R1) behind the right lower molars, tube moves posteriorly, penetrating structures on the left side, from condyle forward to premolar area. At canine-premolar region, there is a change of rotational axis to R2 behind the lower anterior teeth. The anterior segment is then penetrated and the image deposited on the sensor or screen film, which may be curved or straight. X-ray tube will continue to move to the left until central beam intersects rotational axis at R3. At this point, the central beam penetrates the right canine-premolar region. Final exposure is done on the R3 axis with the radiation moving posteriorly past the right condyle (Reproduced from Paatero YV. Pantomography orthopantomography[8]).

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In most modern devices [Figure 1b], digital sensors are applicable. To obtain an orthopantomogram, the X-ray source and a narrow area detector (sensor) are coupled as part of an overhead C-arm. The pattern of the X-ray photon is fan-shaped, and it is collimated to the mounted detector and rotates around the patient's head at a constant speed. The centre of rotation moves along a predetermined path with respect to the sagittal plane.[8],[9] The images so acquired are transmitted to the attached computer for processing and viewing. There is usually software that enables the machine to communicate with other computers. In most instances, it is possible to share digital imaging and communications in medicine (DICOM) images and patient information over the intranet. In some other instances, the requesting clinician may wish to have the analogue copy of the image. DICOM compatible printers can be installed for this purpose.
Figure 1b: The gantry of Planmeca 2D S3 with Protouch®. The X-ray source, the digital narrow detector, and various patient positioning aids are visible (Picture courtesy of the Radiology Department of the Aminu Kano Teaching Hospital, Kano, Nigeria).

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The radiation factor

The narrowness of the X-ray beam and the dynamic nature of the imaging technique create a challenge in assessing the patient radiation dose in orthopantomography. The effective dose is a measurement of the degree of harmful effect on the human body of a particular type of radiation. It is used to estimate the radiation risk (measured in Sievert [Sv] or milli-Sv) which is the possibility of biological consequences after radiation exposure. The effective dose of orthopantomograph is about 6.7 μSv with a range of 3.0–15.6 μSv.[10],[11],[12] The radiation received by the patient is considerably less from the orthopantomograph than from conventional periapical examination.[7],[10],[11],[12] Gonadal dose to the patient is also minimal for orthopantomography.[10],[13] For quality control purposes, dose-width product (DWP) is a useful parameter. It uses film to assess dose and to measure beam width. The value obtained is a reflection of the radiological parameters (mA, kVp, and time) used to optimise the density of the resultant image.[14] Dose-area product (DAP) is linearly related to the product of mA, KVp, and beam area. According to Williams and Montgomery,[14] the average DAP for orthopantomograph is 11.3 cGycm 2, with a range of 4.7–15.3 cGycm 2. The adopted reference value for DWP is 65 mGy mm for the standard adult orthopantomograph.[14],[15] The DAP is a better parameter for assessing the relative risk patient is exposed to while undergoing an exposure for an orthopantomograph.[14],[15] Both the DAP and the DWP are measured with the use of a thermoluminescent dosimeter, and the principal determinant of dose is the film-screen speed.[15]

The advantages of orthopantomography include the wide coverage of the oral structures, relatively low radiation exposure and moderately low expense of the equipment. It has limitations including lower resolution, higher distortion and potential overlap of anatomical structures. The image quality is related to bone density, and it may be difficult to accurately identify vital structures.[16]

Imaging anatomy

The lateral walls of the nasal cavity are depicted in the midline of the radiograph, sandwiched between the images of the orbit on either side and the roof of the mouth. The outline is radiopaque and somewhat symmetrical. The floor of the nasal fossae coalesces into the anterior nasal spine which appears markedly radiopaque [Figure 2]a and [Figure 2]b.
Figure 2: (a and b) The outline of the lateral wall of the nasal fossa is depicted by the red line.

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The highly variable anatomy of the lateral nasal wall [17],[18] makes the region vulnerable for complications during endoscopic surgery. The conchae (turbinates) are the most prominent feature of the lateral nasal wall. They are usually three and appear as scrolls of bone.[19] The turbinates are referred to as conchae when they are pneumatised. The inferior conchae are a separate bone, and it is derived embryologically from the maxilllo-turbinal bone.[20],[21],[22],[23]

The nasal septum, representing mainly the perpendicular plate of the ethmoid, vomer, and septal nasal cartilage,[24] is seen as a midline radiopacity. The bony perpendicular plate of ethmoid runs superiorly from the crista galli through the cribriform plate of the ethmoid bone.[24] Inferiorly, it anchors on the roof of the palate and the anterior nasal spine. The nasal septum may sometime appear enlarged. In this case, it is referred to as septal tumescence [Figure 3]. The nasal septum plays a paramount role in determining nasal aesthetics and nasal function. A firm understanding of the anatomic and physiologic aspects of the nasal septum will allow the surgeon to better appreciate the challenges of nasal reconstruction.[25]
Figure 3: Outline of an enlarged nasal septum.

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The floor of the nose, and additionally, the nasal opening of the nasolacrimal duct open in the anterior third of the inferior concha.[26] There is a mucosal valve named Hasner's valve covering this opening.[20],[21] The most prominent on the orthopantomograph is the inferior conchae. It lies mediolaterally as a solid radiopaque entity, somewhat spanning the lateral wall of the nasal cavity and the inferior component of the superimposed maxillary sinus. The inferior conchae are like a sea shell. It is, therefore, not uniformly solid. The diagnostic significance is recognising it as an anatomical structure in evaluating the pathoses of the nasal cavity and maxillary sinus, especially fibro-osseous lesions [Figure 4].
Figure 4: The red arrows outline the anterior and superior boundaries of the left inferior conchae. The right inferior conchae can easily be appreciated.

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Soft tissues of the nose portray as radiopaque entities on either side of the intermaxillary suture line. When visualised, it is often a uniformly rounded radiopaque entity in close proximity of the apices of the maxillary incisors. The tip of the nose may portray as a midline structure between the roots of the maxillary central incisors. This radiographic appearance can be misconstrued as a mesiodens [Figure 5] and [Figure 6].
Figure 5: Arrow indicates the soft tissue of the nose.

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Figure 6: Solid arrow indicates the tip of the nose.

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The maxillary sinus is also called antrum of Highmore or maxillary antrum [23] and is the hollow, reversed pyramidal cavity occupying the maxilla on either side.[23] On the orthopantomograph, the outline of the maxillary sinus is thinly radiopaque, extending from, and sometimes overlapping, the lateral wall of the nasal cavity anteriorly, extending superior-inferiorly in the proximity of the orbit to the pterygomaxillary fissure. The floor of the maxillary sinus, radiographically, is portrayed as draping over the roots of the posterior teeth, in particular, the molar teeth. The diagnostic value of the maxillary sinus includes evaluation of cystic lesions, foreign body impaction such as displaced root fragments, metallic foreign bodies, antroliths, benign soft and had tissue lesions and antral malignancies [Figure 7]. The maxillary sinus is closely linked to the alveolar crest. The resorption of alveolar crest in edentulous individuals can impact implant planning. Invariably, there will be a need for sinus lift procedure aimed at reducing the expanded volume of the maxillary sinus partially or totally.[27]
Figure 7: The visualised borders of the right maxillary sinus are outlined.

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The zygomatic (sometimes called temporal) process of the maxilla is the bony projection of the maxilla, extending backward to join the zygomatic process of the temporal bone.[26] On the orthopantomograph, it is portrayed as a V-shaped, U-shaped or J-shaped radiographic entity, extending inferolaterally from the orbital rim at the anterior limit of the zygomatic bone [Figure 8].
Figure 8: The visualised portion of the right zygomatic process of the maxilla is portrayed with the red markings.

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The zygomatic arch is the slim bony bridge extending from the zygomaticomaxillary suture anteriorly to the zygomaticotemporal suture posteriorly.[26] On the orthopantomograph, the inferior border can be appreciated from the zygomatic process of the maxilla to the articular eminence of the TMJ. While orthopantomograph is not the ideal imaging modality for reviewing fractures of the zygomatic arch (submentovertex projection being preferred), such fractures can be appreciated on the orthopantomograph, especially if the two arches are compared bilaterally. It is important to appreciate the zygomaticotemporal suture so that it is not interpreted as a fracture line [Figure 9]. The zygomatic complex, comprising the zygomatic bone and the zygomatic arch, bears the brunt of resistance to violence from many directions. By its prominence, it plays a great role in protecting the eye from impact.[28]
Figure 9: The visualised portions of the right zygomatic arch as outlined by the arrows.

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The orbital rim is visualised on the orthopantomograph as a radiopaque line running superoinferiorly to contact the zygomatic process of the maxilla. The line runs mediosuperiorly in the proximity of the lateral wall of the nasal cavity. The portrayed outline of the orbital rim is useful in assessing zygomatic complex fractures. Closely related to the infraorbital rim is the cylindrical entity bordered by two radiopaque lines. This entity represents the infraorbital canal. A neurovascular bundle traverses this canal [24],[26] and is a landmark for infraorbital nerve anaesthesia [Figure 10].
Figure 10: The outline of the right orbital rim is portrayed by the red line.

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The clinical significance of the orbital rim includes eyelid support, maintaining position of the content of the orbit and cosmesis. The fracture involving the orbital rim requires specific clinical and radiologic evaluation for detection.[29],[30]

The pterygomaxillary fissure is an anatomic landmark of the interval between the pterygoid processes of the sphenoid bone and the posterior segment of the maxilla and the maxillary tuberosity [24],[26] which is portrayed as a reverse tear drop-shaped entity. The maxillary artery enters the pterygopalatine fossa through the pterygomaxillary fissure. The corresponding vein opens into the large pterygoid plexus located in the infratemporal fossa between the temporalis muscle and lateral pterygoid muscle [28] and are of great concern for copious haemorrhage during total maxillectomy procedures [Figure 11].
Figure 11: The outline of the right pterygomaxillary fissure is indicated by the red line. The arrow shows the position of the left pterygopalatine fissure.

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The maxillary nerve trunk exits the cranial base through the foramen rotundum into the pterygopalatine fossa that lies in the posterior aspect of the maxilla. This region is at the base of the pterygoid plates and is associated with the pterygomaxillary fissure.[26] It is suggested that maxillary nerve block anaesthesia can be achieved by depositing local anaesthetic agent in the proximity of the nerve in the pterygomaxillary fissure.[31],[32] Infiltration anaesthesia is the often taught technique for anaesthesia of the maxillary teeth. However, in certain circumstances, such as dentoalveolar abscess, or persistent pain during endodontics, it is possible to adopt a new technique for anaesthetising the maxillary nerve.

The external auditory meatus is visualised as an oval, radiolucent entity immediately posterior to the head of the condyle. In maxillofacial practice, it remains significant in the assessment of the TMJ being useful in the orientation and interpretation of TMJ images [Figure 12].
Figure 12: The right external auditory meatus is indicated by the red line while the contralateral side is easily visualised.

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The stylohyoid complex is visualised on the orthopantomograph. The stylohyoid complex comprises the styloid process of the temporal bone, stylohyoid ligament and hyoid bone.[24] The stylohyoid ligament attaches the styloid process with the lesser cornu of the hyoid bone, and this ligament can ossify to different degree, resulting in varying length of the styloid process. The average length of the styloid process is 2.5 cm.[33],[34] The hyoid bone is located between the mandible and the larynx and consists of a body and a lesser and greater cornua.[26] The stylohyoid complex assumes clinical significance when the stylohyoid ligament is ossified bilaterally. Eagle's syndrome is characterised by elongated styloid process with associated pharyngeal pain and referred otalgia occurring after tonsillectomy. It is easily diagnosed on a routine examination of an orthopantomograph. In addition, the stylohyoid complex plays a part in phonation.[33],[34],[35] The differences in the morphological features of the hyoid apparatus and pharynx between the subfamilies of the Felidae have an influence on the specific structural characteristics of their vocalisation.[33] The anatomy of the hyoid apparatus has important implications for vocal tract length; hence, specific structural characteristics for species vocalisation. There is a degree of correlation between the degree of ossification of the hyoid bone and the presence or absence of purring and roaring in various animal species.[36] The hyoid bone dimension is significantly larger in men than in women. The female hyoid has relatively long and thin distal segments, and this may increase susceptibility to fracture.[37] The hyoid bone is, therefore, of considerable forensic interest owing to its susceptibility to fracture during manual strangulation [38] [Figure 13].
Figure 13: The outline of the hyoid bone is indicated by the arrows.

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The floor of the nose, roof of the mouth, soft palate and tongue are visualised on the orthopantomograph. In making the orthopantomograph, patients are often instructed to put their tongue against the roof of the mouth. This procedure eliminates the air column between the tongue and the palate. Where this is not done, the air column appears radiolucent and could prevent adequate interpretation of dental caries in the maxillary teeth. The base of the tongue can be visualised as the soft palate lies against it in the upper aerodigestive tract [Figure 14].
Figure 14: The outline of the soft palate is indicated by the arrows.

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The entire outline of the mandible is clearly visualised on the orthopantomograph [Figure 15]. This imaging modality is useful in the assessment of pathoses of the mandible including third molar impaction and osseous lesions.
Figure 15: The inferior alveolar canal can be easily visualised on the orthopantomograph. This assessment is useful in determining the proximity of the roots of the impacted third molars to the neurovascular bundle. It is not unusual for the superior border to be discontinuous.

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  Conclusions Top


Orthopantomograph is the most common and basic imaging technique for evaluation of new dental patients and management of maxillofacial traumas, cysts and tumours. A good knowledge of the anatomy as visualised on the image is a responsibility of the prescribing clinician and it better serves the good health of the patient. The knowledge of maxillofacial anatomy on the orthopantomograph can be challenging due to distortion and superimposition of anatomic structures. However, a good understanding of the normal enables the clinician to identify the abnormal.

Acknowledgements

The authors are grateful to Professor Axel Ruprecht of The University of Iowa College of Dentistry, for making imaging illustrations available for this study. We are also grateful to all the staff of the Oral and Maxillofacial Radiology Department of the institution, who made the radiographs.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1a], [Figure 1b], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15]



 

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